The present invention is an improvement to the current mirror correction circuitry described in patent application Ser. No. 08/638,419, filed Apr. 26, 1996, which application is assigned to the assignee of the present invention. As shown in FIG. 1, such circuit includes first and second pnp transistors 10 and 12 having connected bases. A resistor 14 is connected to the emitter of transistor 10 and a resistor 16 is connected to the emitter of transistor 12. The two transistors are configured to provide voltage tracking across the resistors 14 and 16. Such a current mirror topology has some inherent inaccuracies in that the base-emitter voltage of transistor 12 is not always identical to the base-emitter voltage of transistor 10. For example, for large values of V.sub.s and small values of resistor 14 the base-emitter voltage of transistor 10 will be nearly constant but the base-emitter voltage of transistor 12 will vary with changes in the load current I.sub.1 and thus the current through resistor 16. Therefore, rather than connecting the collectors of transistors 10 and 12 directly to respective resistors, the circuit includes an npn transistor 18 connected in series with the transistor 10 and an op-amp 20 having its input terminals arranged to provide current matching across a pair of like value resistors 22 and 24 in order to provide an output voltage V.sub.1 across resistor 24 which is proportional to the load current I.sub.1.
However, such circuit is relatively complex and op-amps are relatively expensive. It would therefore be desirable to provide a circuit which enables current matching across a pair of like value resistors with a reduced number of parts so as to reduce costs. There also exists a need to accurately measure rapidly changing high currents on the high side of a load being driven by a high voltage. It would therefore be desirable to provide a circuit which responds faster to changes in the load current.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.